Circulating Currents in Electric Machines: Positive Impact of The End Windings Length on Losses

TL;DR

This paper demonstrates mathematically that increasing the length of end windings in electric machines reduces circulating currents and associated losses, supported by a case study.

Contribution

It provides a mathematical proof that longer end windings decrease circulating currents and losses, offering a new design insight for electric machine efficiency.

Findings

Losses decrease proportionally to the inverse square of end winding length

Mathematical proof of the relationship between winding length and circulating currents

Case study validating the theoretical results

Abstract

Circulating currents occurring in windings of electric machines received rising interest recent years. Circulating currents represent unwanted currents flowing between parallel-connected conductors. This phenomenon is due to various reasons such as asymmetries in the winding and differences in electric potential between parallel-connected conductors. This effect occurs both at no-load and on-load conditions, and always lead to uneven distribution of the current between the parallel conductors, therefore leading to higher losses, as proven in the authors' previous work. Circulating currents are occurring mainly due to asymmetries and electric potential difference in the active part, meaning that long end windings are advantageous to mitigate the effect of circulating currents. Losses due to circulating currents decrease at a rate proportional to the inverse square of the end windings length. The aim of this paper is to mathematically prove this property and present a case study application in an electric machine.